In 3GPP release 6, the WCDMA specifications are extended with a new uplink transport channel, the Enhanced Dedicated Channel (E-DCH), including Enhanced Dedicated Physical Data Channel (E-DPDCH) and Enhanced Dedicated Physical Control Channel (E-DPCCH). The gain factors for E-DPDCH, βed, which is used to indicate the power offset between E-DPDCH and DPCCH channels, is very important for uplink system performance as it determines how much power would be allocated to data channel E-DPDCH for certain transport block size. Too much power to E-DPDCH would result in much interference and affect other users' performance; on the other hand, too low power to E-DPDCH would affect the quality of this user itself.
Depending on the amount of data to be transmitted on the data channel, the transport format is different. For different transport format, to get the desired transmission error performance, for example, BLock Error Rate (BLER), the required power is different. Therefore, the power offset depends on the transport format used on the data channel. Usually there is a table to describe the relationship between the transport format and the required power offset.
The Node B and the user equipment (UE) both need to know this table for scheduling and transport format selection. Currently, the table index is signalled to the UE. When the number of transport formats is large, signalling all gain factors for the whole table requires large signalling overhead. Therefore, usually, only several transport formats are selected as reference transport formats, and their gain factors are signalled to the UE. For other non-reference transport formats, their gain factors need to be calculated by either interpolation or extrapolation based on the signalled gain factors of the reference transport formats. The gain factors of these reference transport formats can be obtained by link-level simulations.
According to 3GPP 25.331, other gain factors need to be calculated according to the reference E-DPDCH gain factors as below.
                              β                      ed            ,            j                          =                              β                          ed              ,              ref                                ⁢                                                    L                                  e                  ,                  ref                                                            L                                  e                  ,                  j                                                              ⁢                                                    K                                  e                  ,                  j                                                            K                                  e                  ,                  ref                                                                                        (        1        )            
Where Le,ref and Le,j are the number of E-DPDCHs used for the reference E-DCH Transport Format Combination (E-TFC) and the j:th E-TFC respectively. Ke,ref and Ke,j denote the transport block size of the reference E-TFC and the j:th E-TFC respectively.
The reference gain factors βed,ref are calculated from the signalled power offset, ΔE-DPDCH, according to
                              β                      ed            ,            ref                          =                              β            c                    ·                      10                          (                                                Δ                                      E                    -                    DPDCH                                                  20                            )                                                          (        2        )            where the value ΔE-DPDCH in UE is signalled from the network. In current specification, its range is between [0, 1, . . . , 29].
In 3GPP Release 7, there is a new interpolation based formula defined for uplink E-DPDCH gain factor for higher bit rates after introducing 16QAM. In current 3GPP specification, it is allowed to signal up to 8 reference gain factors from the network to UE.
Using these limited reference gain factors (at most 8 values in current specification) for calculation of many E-DCH Transport Format Combination Indicators (E-TFCIs) (more than 100) will lead to less accurate and thus less efficient E-TFCIs. For example, for VoIP services, the selected E-TFCIs are usually small while for uploading services, the selected E-TFCIs are usually large. If the limited reference values are signalled to UE probably favourable for VoIP services, obviously the selected E-TFCIs for uploading services may be subject to much inaccuracy, and vice versa. In addition, as the current reference value is a quantized value, there is a quantization error and it is in fact not small in some sense. For example, if a βed/βc value of 57 is needed, we have to use a βed/βc value of either 53 or 60 by signalling ΔE-DPDCH of either 19 or 20.
Another problem in existing solutions is that the reference gain factors have to be signalled to UE via a Radio Resource Control (RRC) whenever UE has a session setup to the network via Enhanced Uplink (EUL), regardless whether or not the reference gain factors have been signalled to the UE before. The current situation is that after releasing a RRC connection, maybe the network will with almost 100% certainty set up exactly the same RRC connection with the same reference factors. Actually, these reference factors maybe not necessary to be signalled to UE for many times at least in one vendor's UMTS Terrestrial Radio Access Network (UTRAN) system or one of its product versions. On the other hand, the current signalling mechanism makes signalling the whole table almost impossible due to much overhead increasing a session setup delay.